Head up displays for motor vehicles

Abstract: A head up display system (10) for a motor vehicle includes a sensor (11), display means (20) for forming a video image from the signals received from the sensor (11) and a projection system (22, 24, 25, 26) for projecting the video image onto the windscreen (12) of the vehicle, the projection system (22, 24, 25, 26) including a mirror (26) for deflecting the optical path of the projected image, said mirrors (26) being located directly in front of a driver of the vehicle at a level outside the normal field of view of the driver through the windscreen (12), the mirror (26) being arranged; in a head up display mode, to direct the projected image onto the windscreen (12); and in a non-head up display mode, to permit direct viewing of the video image at a level outside the normal field of view of the driver through the windscreen (12).

Description: The present invention relates to head up displays for motor vehicles. It has been proposed to provide a head up display for a motor vehicle in which an enhanced view of the road ahead is projected onto the vehicle windscreen, so that it is overlaid onto the drivers view of the scene. In this manner, potential hazards which may not be clearly visible to the driver, may be highlighted. In order to ensure that the objects within the image appear to the driver to be the same size as the objects in the real scene, the field of view of the sensor is matched to the field of view which the driver has of the display. The image is then projected into the relevant area of the driver's forward line of sight and is arranged such that the driver's own view of the objects is overlaid with the images of the objects generated from the sensor, processing and display combinations. To produce an overlaid image of this type, a large field of view is required. Within the constraints of the motor vehicle which places limitations on the size of the video display device which may be used and the optical path length of the projected image, this may be achieved by the use of a mirror which will bend the optical path. This will also allow the display device to be positioned behind the dashboard of a vehicle, the mirror serving to deflect the projected image onto the windscreen. The centre line of the projected image and the centre line of the driver's forward field of view must also be coincident. As a result, the mirror used to deflect the projected image onto the windscreen must be positioned directly in front of the driver at a level below the level of the windscreen. That is, in a position conventionally used for the vehicle instrument display. The positioning of a mirror in this way will consequently significantly reduce the area available for vehicle instrument display. WO-A-87 106017 discloses a head up display system for an aircraft which also provides head down displays for instrumentation. However in accordance with the disclosure in this specification separate video image display devices are required for providing the head up and head down displays which would present packaging problems in the confined space available in a motor vehicle. US-A-3885095 discloses a head up display system for aircraft in which the same video image is displayed in head up and in head down display mode. This does not overcome the instrumentation problem addressed by the present invention. GB-A-1409743 discloses a head up display system for aircraft in which a reflector reflects the head up display into the view of the pilot while instrumentation data may be transmitted through a mirror for viewing in a head down display mode. This system does not however disclose the projection of a head up display onto the windscreen of the airplane and would not be capable of providing an image which could be overlaid on the view of the driver ahead of the vehicle. According to one aspect of the present invention a motor land vehicle has a head up display system, said head up display system comprising: sensor means for sensing the scene ahead of the vehicle; image display means for forming an image of the scene ahead of the vehicle from signals received from the sensor means; and projection means for projecting the image of the scene ahead of the vehicle onto the windscreen of the vehicle, so that when viewed by a driver of the vehicle, the image of the scene ahead of the vehicle projected onto the windscreen will be superimposed on the scene ahead of the vehicle as viewed through the windscreen, characterised in that second input means is provided by which the image display means (20) will also provide a flexible format display different from the scene ahead of the vehicle; said projection means including a mirror, said mirror being located between the image display means and the position of a driver in the vehicle and directly in front of the driver at a level outside the normal field of view of the driver through the windscreen, said mirror reflecting light of wavelengths within a first band of wavelengths and transmitting light of wavelengths outside said first band of wavelengths; the image of the image display means being projected onto the mirror so that the image of the scene ahead of the vehicle is reflected by the mirror onto the windscreen of the vehicle, while the flexible format display is transmitted by the mirror where it may be viewed directly by the driver, in a head down display mode. In accordance with the above described invention, when in the head up display mode the system will project the projected image onto the windscreen. However, in a non-head up display mode, the means for forming a video image may be used to provide a flexible format display which may form part of the conventional instrument display of the vehicle. This flexible format display may be used, for example, to display operating parameters of the vehicle, navigational information and/or views to the rear or sides of the vehicle for manoeuvring purposes. The mirror is preferably located at a level below that of the windscreen. According to one embodiment of the invention, the mirror is a narrow band reflector, so that only light in a narrow waveband is reflected onto the windscreen. This form of mirror may be used with a light source emitting light within the narrow band, when in the head up display mode and a second light source emitting light outside the narrow band when in the non-head up display mode. However, preferably wide band light source is used in both modes, shutter means being provided to intercept the reflected light when in the non-head up display mode. An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings in which:- Figure 1 is a partial sectional elevation of a motor vehicle with head-up display in accordance with the present invention; Figure 2 is a plan view of an instrument panel of a vehicle fitted with a head-up display in accordance with the present invention; and Figure 3 is a sectional elevation of the head-up display system used in the vehicle illustrated in Figure 1. As illustrated in Figure 1, the head up display system 10 of the present invention projects an image onto the windscreen 12 of the vehicle, which coincides with the driver's view of the scene ahead of the vehicle. The head up display is arranged such that images produced by the head up display system are overlaid onto the objects viewed directly by the driver. As illustrated in greater detail in Figures 2 and 3, the head up display system 10 includes a mirror 26 which reflects a projected image onto the windscreen 12. The mirror 26 is adapted to permit the passage of a projected image when the head up display system is not on, to provide a flexible format display which may be viewed in a head down display mode. As illustrated in Figures 2 and 3, the head up display system 10 comprises a liquid crystal display 20 which converts signals from a sensor 11 which looks forwardly of the vehicle, into a video image. The sensor may operate in the infra-red, visible and/or ultra-violet wavelengths and the signals therefrom are processed to enhance the image. The liquid crystal display 20 is illuminated by a wide band light source 22 and a lens system 24, 25 projects the video image produced by the liquid crystal display 20 onto a narrow waveband mirror 26, which is located centrally of the vehicle instrument panel 30 as illustrated in Figure 2. The mirror 26 reflects light within the narrow waveband upwardly through an exit lens 28 and onto the windscreen 12. Light of wavelength outside the narrow waveband of mirror 26 is transmitted through the mirror 26 to provide a flexible format display which may be viewed on the reverse side of the mirror 26. In the head up display mode of operation, the video image produced by the liquid crystal display 20 is reflected onto the windscreen 12 by mirror 26, so that it may be viewed by the driver. A display of reduced colour range of the image is also transmitted through the mirror 26 and may be viewed by the driver in a head down display mode. When the head up display is switched off, a shutter 27 is placed over the exit lens 28, so that no image is projected onto the windscreen 12. The shutter 27 also prevents reflections from the optical system of the head up display system which would otherwise be reflected onto the windscreen 12. The shutter 27 may, for example, be a layer or solution of electrochromic material controlled electronically, or may be a mechanically controlled shutter. When the shutter 27 is closed, the liquid crystal display 20 may be used in a flexible format display mode, to provide a reduced colour range display on the reverse side of the mirror 26 which may be viewed in a head down display mode. This flexible format display may be used to display vehicle parameters and symbols, navigational information or other similar data. In the embodiment illustrated above, only the central part of the mirror 26 need be used for head up display purposes. The top and bottom regions 32 and 34 may for example be arranged to transmit light over the full visible spectrum and the corresponding regions 35, 36 of the liquid crystal display 20 may give a permanent display of vehicle parameters or symbols which will be displayed in the full colour range, on the reverse side of the mirror 26, whether the head up display is functional or not. Such information may be in the form of an array of warning lights corresponding to various parameters of the vehicle. The liquid crystal display 20 may furthermore be used to superimpose warning messages on the windscreen when in the head up display mode. Such messages should not however unduly distract the drivers attention from the road. This mode of operation of the system may be used, for example, to give warning of failure of vital systems of the vehicle, collision avoidance information or indications for turning the vehicle generated by navigational systems. Various modifications may be made without departing from the invention. For example, while in the above embodiment the video image is produced by a liquid crystal display, other display devices which will create an image which may be projected for example, cathode ray tubes, ferromagnetic displays or plasma displays, may be used. Furthermore, in place of a narrow waveband mirror, an electronically controlled electrochromic mirror or mechanically moved mirror may be used.

Claims: A motor land vehicle having a head up display system (10) said head up display system comprising: sensor means (11) for sensing the scene ahead of the vehicle; image display means (20) for forming an image of the scene ahead of the vehicle from signals received from the sensor means (11); and projection means (22,24,25,26) for projecting the image of the scene ahead of the vehicle onto the windscreen (12) of the vehicle, so that when viewed by a driver of the vehicle, the image of the scene ahead of the vehicle projected onto the windscreen (12) will be superimposed on the scene ahead of the vehicle as viewed through the windscreen (12), characterised in that second input means is provided by which the image display means (20) will also provide a flexible format display different from the scene ahead of the vehicle; said projection means (22,24,25,26) including a mirror (26), said mirror (26) being located between the image display means (20) and the position of a driver in the vehicle and directly in front of the driver at a level outside the normal field of view of the driver through the windscreen, said mirror (26) reflecting light of wavelengths within a first band of wavelengths and transmitting light of wavelengths outside said first band of wavelengths; the image of the image display means (20) being projected onto the mirror (26) so that the image of the scene ahead of the vehicle is reflected by the mirror (26) onto the windscreen (12) of the vehicle, while the flexible format display is transmitted by the mirror (26) where it may be viewed directly by the driver, in a head down display mode. A motor land vehicle according to claim 1 characterised in that the mirror (26) is located at a level below the level of the windscreen (12). A motor land vehicle according to any one of claims 1 to 3 characterised in that the projection means (22, 24, 25, 26) includes a wide band light source (22), light of wavelengths corresponding to the first band being reflected by the mirror (26) onto the windscreen (12) while light of wavelengths outside that of the first band are transmitted through the mirror (26). A motor land vehicle according to Claim 4 characterised in that shutter means (27) is provided, to be located between the mirror (26) and windscreen (12) to intercept the projected image, when the head up display (10) is switched off. A motor land vehicle according to Claim 5 characterised in that the shutter (27) is provided by an electronically controlled electrochromic layer or solution. A motor land vehicle according to Claim 5 characterised in that a mechanical shutter (27) is moved into the path of the projected image when the head up display system is switched off. A motor land vehicle according to any one of claims 1 to 3 characterised in that , in the head up display system mode, the projected image is produced by a narrow band light source (22) corresponding to the narrow band reflector. A motor land vehicle according to any one of the preceding claims characterised in that the means (20) for generating a second video image may be used to produce a flexible format display, to be viewed at a level outside the normal field of view of the driver through the windscreen (12), in the head down display mode. A motor land vehicle according to any one of the preceding claims characterised in that the device (20) for forming a video image is a liquid crystal display, cathode ray tube, ferromagnetic display or plasma display. A motor land vehicle according to any one of the preceding claims characterised in that the mirror (26) is arranged to permit passage of a portion of the projected image whether the head up display system is functional or not, the means (20) for forming the video image being used to produce a permanent display corresponding to said portion of the projected image. A motor land vehicle according to Claim 9 or 11 characterised in that the display (20) provides a display of vehicle parameters and symbols, navigational information and/or views to the rear or sides of the vehicle for manoeuvring purposes. A motor land vehicle according to any one of the preceding claims characterised in that the means (20) for forming a video image is arranged to superimpose warning messages on the windscreen (12), when the system is in the head up display mode.

Inventors: MULVANNY PAUL, WILLIAMS MALCOLM, MULVANNY, PAUL, WILLIAMS, MALCOLM
Applicants: JAGUAR CARS, JAGUAR CARS LIMITED
Application year: 1994
Main classification: G02B27
IPC codes: B60K35, G02B27, B60K37, G02B5, G01D7